Fix iOS orderByKey() crash with startAt()/endAt() — use 1-param native method when key is null

[Copilot]

On iOS, orderByKey() combined with startAt()/endAt() crashes with InvalidQueryParameter: You must use queryStartingAtValue: instead of queryStartingAtValue:childKey: when using queryOrderedByKey:. The Apple implementation unconditionally called the 2-parameter ObjC methods even when key was null.

• startAt(), endAt(), equalTo() (all 3 type overloads each): dispatch to the 1-parameter native method (queryStartingAtValue:, queryEndingAtValue:, queryEqualToValue:) when key is null, and the 2-parameter version (queryStartingAtValue:childKey:, etc.) when key is provided.

// Before — always calls queryStartingAtValue:childKey:, crashes with orderByKey()
Query(ios.queryStartingAtValue(value, key), persistenceEnabled)

// After — dispatches correctly based on key nullability
Query(if (key == null) ios.queryStartingAtValue(value) else ios.queryStartingAtValue(value, key), persistenceEnabled)

• Integration tests added in commonTest to validate orderByKey() with startAt()/endAt():
  • testOrderByKeyWithStartAtAndEndAt — prefix matching using both startAt() and endAt() (reproduces the original crash scenario)
  • testOrderByKeyWithStartAt — orderByKey() with startAt() only
  • testOrderByKeyWithEndAt — orderByKey() with endAt() only

Original prompt

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This section details on the original issue you should resolve

<issue_title>iOS: orderByKey() with startAt()/endAt() crashes - uses wrong native method</issue_title>
<issue_description>## Bug Description
Using orderByKey() with startAt() or endAt() crashes on iOS with:

InvalidQueryParameter: You must use queryStartingAtValue: instead of 
queryStartingAtValue:childKey: when using queryOrderedByKey:

Reproduction

database.reference("Videos")
    .orderByKey()
    .startAt("prefix_")
    .endAt("prefix_\uf8ff")
    .valueEvents
    .first()

Environment

• GitLive Firebase Kotlin SDK: 2.4.0
• Platform: iOS
• File: firebase-database/src/appleMain/kotlin/dev/gitlive/firebase/database/database.kt

Root Cause

The iOS implementation incorrectly calls queryStartingAtValue:childKey: (2-parameter version)
instead of queryStartingAtValue: (1-parameter version) when using orderByKey().

Workaround

Fetch all data and filter client-side.

Expected Behavior

Should work like Android, using database-side filtering efficiently.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes iOS: orderByKey() with startAt()/endAt() crashes - uses wrong native method #798

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[Reedyuk]

@nbransby - need approval please, "At least 1 approving review is required by reviewers with write access. Approvals from users that collaborated with the coding agent on changes will not satisfy review requirements."

[Reedyuk]

@copilot can you create unit tests too

[Copilot]

@copilot can you create unit tests too

Added three integration tests in commit 1b412a6:

• testOrderByKeyWithStartAtAndEndAt — prefix matching using both startAt() and endAt() with orderByKey() (reproduces the original crash scenario)
• testOrderByKeyWithStartAt — orderByKey() with startAt() only
• testOrderByKeyWithEndAt — orderByKey() with endAt() only